Patterning a substrate is critical to fabrication of integrated circuits and data storage media. The limitations of conventional lithographic patterning for dimensions below 0.1 micron (100 nm.) are well known, and are described in "Lithography for ULSI", by S. Okazaki, in a review paper (p. 18, vol. 2440, Proceedings of SPIE). Optical lithography with a light source in the deep ultra-violet ("DUV") is expected to serve in circuit and media fabrication for feature sizes down to about 0.05 micron (50 nm), but not for smaller sizes. At present, there are no inexpensive methods for lateral patterning/texturing of solid substrates on a 1 to 50 nm scale, which is much smaller than the present lithographic feature size.
DUV optical lithography is currently anticipated to be extended to lateral dimensions of .about.50 nm, but such extension is not certain and may be expensive. At dimensions below .about.50 nm X-ray lithography and Extreme UV lithography are being considered but both require enormous capital investments (both for the radiation sources and the supporting optical systems). Direct write systems including electron beam and scanning probe based lithography are in development, but the serial nature of the patterning process makes these prohibitively slow for manufacturing. Microcontact printing and nano-imprint lithography are new patterning techniques which hold some promise in and around 50 nm feature sizes but these methods are not well proven at the present. It would be desirable to have an inexpensive, large area, method for lateral patterning that does not require lithography, and that is suitable for feature sizes below 50 nm.
In the case of magnetic storage media, for example tapes and disks having coatings of magnetic particles thereon, a number of difficulties prevent attainment of high densities. For example, where the usual coatings of magnetic particles are applied on flexible media, wide variations in individual particle diameters raise the minimum information bit storage size, and thus decrease the attainable areal information bit storage density. In the case of conventional rigid magnetic storage media, sometimes called "hard drive" disks, magnetic films are often applied by sputter deposition. The resultant broad distribution of grain sizes and inter-granular spacings creates both low effective areal bit densities and undesirably low signal-to-noise ratios. Even where magnitudes and uniformity of the diameters of the particles is acceptable, the strong magnetic interaction of the particles often causes significant increases in minimum information bit storage size due to agglomeration of mutually magnetically attractive particles into clumps of particles, thereby decreasing attainable areal information storage bit density (e.g. as measured in bits per square inch). In fact, currently attainable areal information storage bit densities are about 10 gigabits per square inch although some developers hope to achieve 40 gigabits per square inch by the year 2010 A.D.
Methods to make monodisperse magnetic particles (cobalt, for example) with a diameter in the 5-50 nm range have been described by Murray et al in the aforementioned U.S. patent application Ser. No. 09/127,005, now pending, filed simultaneously herewith. Specifically, this Murray et al patent application describes formation of magnetic cobalt (Co) particles with mean diameter D, where D=8 to 10 nm., and with a standard deviation in the size distribution of 5%.
Methods for self-assembly of 40-70 nm. particles made of latex or other polymer are described by Micheletto et al in Langmuir, 1995, v. 11, p 333 and by Du et al in Langmuir, 1997, v. 11, p. 2538. A general method to form a thin film of small particles is described by Nagayama in U.S. Pat. No. 5,505,996. Moreover, formation of ordered arrays of 5-10 nm size semiconductor particles is described by Murray et al in Science, 1995, v. 270, p. 1335 and by Dabbousi et al in Chemistry of Materials, 1994, v.6, p.216. None of the prior art references teach magnetic storage media nor methods of making ordered arrays from particles that have strong magnetic interactions which cause agglomeration and other problems.